Conversion of hydrocarbons



y 1939. H. TRoPscH Re. 21,073

I CONVERSION OF HYDROCAHBONS Original Filed Dec. 15, 1933 INVENTOR HANST PSCH Reiseued May 2, 1939 UNITED STATES PATENT OFFICE Hans 'lropsch,deceased, late of Chicago, Ill., by

Carl W. yon Helmolt, Chicago, 11]., administrator de bonis non,assignorto Universal Oil Products Company, Chicago, 111., a corporationof Delaware Original No. 2,069,785, dated February 9, 1937,

Serial No. 702,433, December 15, 1933. 'Application for reissue August1, 1938, Serial No.

This invention relates more particularly to the conversion of thepropane-butane fractions of hydrocarbon gas mixtures such as, forexample,

natural gas, gas mixtures produced incidental' to the primarydistillation of crude petroleums and the fixed gases produced incracking operations upon heavy hydrocarbon oils. The term"propane-butane fraction is thus intended to include fractionscontaining the corresponding olefins, (propylene and the butylenes)which will constitute a varying proportion 0! cracked gases. It is alsointended to include fractions produced from stabilizer units operatingupon either straight run or cracked gasolines which have the approximatecomposition of propane-butane mixtures although the boiling range may besomewhat wider in these cases due to crude fractionation, e. g. maycontain small percentages of lo'wer boiling members of the group such asethane and methane and some higher boiling members, such as pentane.Pentanes and amylenes representing five carbon atom hydrocarbons are notobjectionable in charging stocks to be treated by the present invention,but it is preferred that methane and ethane be absent or only minoramounts be present as they are distinctly detrimental as will bedeveloped later' in the description.

In a more specific sense the invention is concerned with a pyrolyticprocess for efficiently converting propane-butane fractions intocommercial yields of good anti-knock gasoline, the limiting conditionsof operation under which optimum conversion into desired gasolineliquids is obtained being a particular feature of the process.

The hydrocarbon fractions which serve as the charging material accordingto the present invention are too light for blending in 'gasoline above acertain limit. Also, the total quantities of such gases--produced inpetroleum refining operations, including cracking, is very large (and,from the standpoint of the refiner, they are usually looked upon .as awaste product since, from a fuel standpoint, they are produced in excessof requirements for the heating of cracking processes and frequently forthe total heating of all refinery distilling units, and in many caseslow grade fuels areavailable. 59 A more profitable utilization of thesepropane- 14 Claims. (01.19pm) butane fractions is, therefore, a matterof some importance and the present invention is a contribution to thisfield.

In one specific embodiment the present invention comprises heatinghydrocarbon mixtures 5 consisting essentially of compounds of 3 and 4carbon atoms under selected elevated temperature and pressureconditions, passing the heated products through an enlarged reactionzone in which they are maintained at substantially con- 10 prisingessentially hydrogen, methane, ethane and ethylene which are removedfrom the process, an intermediate fraction consisting essentially of 3and 4 carbon atom hydrocarbons which is returned to the heated zone forfurther (:on- 20 version and liquids of gasoline boiling rangeconstituting the desired product of the'process.

The range and inter-relation of time, temperature, pressure, etc., underwhich the production of/gasoline from 3 and 4 carbon atom hydrocarbonsis accomplished will be brought out in the following description of thesequence of operating steps given in connection with a particular planthookup shown in the attached diagrammatic drawing in whichinterconnected ele- 00 ments are represented by conventional figures inside elevation not drawn to scale.

Referring to the drawing hydrocarbon charging stocks of the generalcharacter previously designated (which will be hereinafter referred 3 toas "propane-butane" mixtures] may be in-'- troduced to the plant by wayof line I, containing control valve 2, and pumped by a pump 3 through aline 4 containing a control valve I into and through a properly designedtubular 40 heating element 6 positioned in a furnace 1. During passageof the gases through the heating element and the subsequent reactionzone, the inter-related factors of temperature, pressure and time are socontrolled that about to by weight of the original charge appears lateras intermediate recycle stock. It has been found that if higher rates ofconversion per pass occur not only is the ultimate yield of liquefiablegasoline hydrocarbons reduced, but also carbon troubles are encounteredin the heating element so that. dangerous overheating oi. the tubes maytakeplace unless frequent shutdown periods are observed. Furthermore, byproper control of the operating conditions while maintaining arestricted conversion per pass, the formation of heavy tars may bepractically eliminated so that these ordinarily useless byproducts ofcracking are not formed. If lower rates of conversion atmospheres,though as a rule when dealing with the commoner propane-butane blends 50to' 75 atmospheres produce optimum results in respect to yield ofgasoline. In regardto temperature, it may be noted that the lower rangesare 5 preferable whenthe gas treated, for example, a

gas from an oil cracking plant, contains a relatively high percentage ofolefins, say from 30 to 40%, while the higher temperatures accomplishmore desirable effects when the olefin content of o the original gasesis low or approximately from 0 to volume concentration. The time underwhich the reacting substances are maintained under these temperature andpressure conditions may vary from approximately 40 to 120 seconds, thisfactor having been found to be related to the olefin content of thegaseous recycle products of the conversion step, which point will bediscussed more at length in connection with the recycle stock.

The heated products from the heating element 6 pass through transferline 8, containing control valve 8, and enter a reaction zone Illwithout substantial pressure reduction other than a slight difierentialdrop due to fluid friction in the line. The reactions of polymerizationwhich occur in this chamber are of an exothermic character and for bestresults the chamber may be cooled somewhat to. maintain the optimumpolymerizirfi temperature for the production of gasoline boiling rangeliquids rather than heavier polymers which are of toohigh boilingrangeforuse ingasoline. The cooling may be brought about by controlledexposure of the chamber to atmospheric conditions or by placing indirectheat exchange coils in the chamber through which if desired the incomingcharge may be pumped countercurrently. 1

The products from the reaction zone comprising fixed gases, gasoline andsmall amounts of heavier polymers is then conducted through line ll,containing control valve II, to a chamber I! provided principally as aseparator for any heavy tars which are settled and withdrawn throughline ll, containing control valve IS. The pressure is preferably reducedat valve I! to some point within the range of 150 to 300 pounds persquare inch, depending upon the relative amoimts of the three types ofproducts, to-wit, gases of two carbon .atoms and less, intermediaterecycle stock eonsistingofcompoundsoi'3and4carbonatoms and gasolinehydrocarbons. Within this pressure range at ordinary temperatures, it isfound that the intermediate recycle stock compounds are liquid eitheralone or at least completely soluble in the condensed gasoline.

The vaporous products from the tar sepazator pass through line l0,containing control valve II, to a fractionator 20 which is operated tofinally separate compounds heavier than gasoline and of the character ofintermediate petroleum distillates which are withdrawn through line ll,containing control valve l9, to any use for which they are suited, whilethe overhead vapors ,comprising the major portion of the admittedproducts pass through line 2|, control valve 22 condenser 23', line 24and valve 25 to receiver 20 which is preferably maintained under thesame pressure as that in the preceding tar separator and fractionator,allowing for differential drops.

Under a; pressure range of approximately 150 to 300 pounds the gaseousproducts present in receiver 20 are found to consist principally ofhydrogen, methane, ethane and ethylene, and as smile the separation issufiiciently sharp so that these gases may be withdrawn more or lesscompletely from the receiver through line Tl, containing control valve28. The removal of the hydrogen and the low molecular weight parafllnsat this point is of positive value while the loss of ethylene is of noconsequence sincethis com- 1.:

pound does not polymerize to any great extent to form gasoline under thepreferred conditions of operation. y

The liquids in receiver 20 comprimng essentially propane, propylene,butanes, butylenes, and liquid gasoline hydrocarbons is then taken by'Dump 3| through line 20, containing control valve and subjected totreatment aimed at the segregation of 3 and 4 carbon atom recycle stockand the desired gasoline product.

The discharge from pump 3! passing'through line I! and control valve 33therein is separated into recycle stock and finished gasoline by any oneof the general methods of stabilization in current use. The question ofthe temperature and pressure employed in the fractionation to removesubstantially all 3 and 4 carbon atom hydrocarbons will depend upontheir percentage in the mixture, the relative proportions of 3 and 4carbon atom compounds, etc. when the percentage of recycle stock isrelatively im they may be removed under substantially'the samepresureasthatobtainingin receiver 20, thatis150to300poundspersquareinch. Inthiscase themixturemaybemildlyheatedduringpassage througha heater coil I4 positioned in the furnace I5 andbrought to a temperature of approximately 100 to 150 F., leaving theheating element through line Ii, containing control valve 31, andentering a fractionator or stabilizer II. By suitably utilizing refluxesin this fractionator the 3 and 4 carbon atom recycle stock may besharply separated from the gasoline so that the vapor pressure of thefinal product is at the required point, usualhr in the neighborhood often pounds per square inch by the Reid vapor pressure test. It is, ofcourse, to be understood that any conventional stabilizer may beemployed.

The overhead products from the fractionator pass through line46,.control valve 41, condenser 48, line 49 and control valve 50 toreceiver 5|, which acts as an accumulator for the recycle fractions. Anyresidue of fixed gases still present at this point may be withdrawnthrough 888 release line 52, containing control fuel if desired.

Recycle stock accumulating in receiver 'II is returnedto the primaryheating element. For best results the combined feed blend of this stockwith the raw feed should comprise not more than valve It, and utilizedas 35% 01 oleflns such as propylene and butylenes. When conditions areproperly regulated in the primary cracking plant this percentage willrarely be exceeded since in most cases an equilibrium seems to beestablished so that the recycle stock contains no more than of 3 and 4carbon atom oleflns, whether the equilibrium is approached from one sideorthe other. If the percentage of higher olefins in the combined feedexceeds this may be reduced by admixing propane-butane mixtures of amore parafilnic character such as would be obtained, for exampie, fromstabilizer units operating upon straight run gasoline. The importance ofthis point resides in the fact that if the olefins in the feed are toohigh there is excessive deposition of carbon in the heating tubes and acorresponding loss in fixed gases of less than 3 carbon atoms under theoptimum conditions of treatment. The recycle stock is returned to theheating zone by way of line 54, control valve 55, recycle pump 56, line5'1 and valve 58 to enter combined feed line 4.

Gasoline representing the final product of the process appears in theplant under description as a bottom reflux from fractionator- 38 fromwhich it, may be withdrawn through line 39, containing control valve 40,to receiver 4| with a.ny necessary intermediate cooling although meansfor effecting this are not shown in the drawing. The receiver isprovided with a gas release line 42 containing control valve 43 and aliquid draw line 44, containing control valve 45, for the re-' lease offinal product.

As exemplifying the relationship obtaining between time, temperature andthe per cent of higher olefins in charging stock within a definitetemperature interval the following data are introduced. In theexperiments furnishing the data, pressure was held constant at 710pounds per square inch,the recycle stock was of the charge and comprisedapproximately 25% of propylene and butylenes. a y

In computing the actual contact time, the following formula was used:

Contact time (seconds) =W where The compressibility of the gases wasignored in these calculations. It was assumed at these high temperaturesthat the perfect gas laws are valid.

The calculated contact time was obtained by using the followingempirical formula:

1og1ot= (7.1140.0105T-0.0112U) logiod where:

t=Reaction time (contact time) in seconds =Temperature in degreescentigrade U=Per cent higher oleflns in the gas. For example U=10 for agas containing 10% higher oleflns.

d=Wgt. per cent of charge not recovered as recycle stock. For example,if 60 wgt. per cent of the charge was recovered as recyc stock, thend='40.

TABL: I

Relation between per cent of gas reacted, olefin content, temperatureand contact time Percent 'lem- Actual Calculated i g g para Percontactcontact 32:5528 olefins cam time time from actual C 4 seconds seconds mm37 500 23. 5 110 98 10. 9 37 5(1) 26. 5 115 120 +4. 35 37 525 37. 5 72+2. 8 37 525 40. 4 75 78 +4. 3 37 525 4D. 6 74 78 +5. 4 28 525 35. 5 10797 --9. 35 28 550 46. 7 67. 7 53 21. 7 28 550 45. 2 66. 2 51 23. D 24525 I 32. B 126 -16. 7 2/4 525 38. 3 143 129 9. 8 24 537 44. 2 96 100+4. 2 24 537 34. 0 86 72 16. 3 24 537 26. 0 67 52 --22 2 24 550 37. 653. 5 49 3. 4 24 550 34. 7 45 45 0 24 550 42. 5 57. 3 58 0 Averagedeviation= 4.5%.

Example I Using a charging stock which contains no olefins, having anaverage molecular weight of 60, gives a combined feed containing 16%higher olefins. This combined feed requires a heating time of 120seconds at 537 C. (1000 F.). At 550 C. (1022 F.) only 75 seconds arenecessary when using apressure of 710 pounds per square inch .in bothcases. In this case a yield of 10 gallons per 1000 cubic feet of gasmixture was obtained, or 300 barrels of gasoline from 1000 barrels ofliquefied charging stock. The liquid product contained 90% gasoline withan A. P. I. gravity of 61.5 at 60 F. and a blending octane number (motormethod) of 93. The Engler distillation of the gasoline fraction follows:

I. B. P. 1" 87 10% 20 124 50 182 90 320 E. P. F 407 Percent over 96.5Percent loss 2.5

Percent bottoms 1.0

I Example II Using a charging stock which contains 37% higher oleflns,and has anaverage molecular weight of 51, gives a combined feed having28% olefins. At 525 C. (977 F.) a time factor of seconds is necessarywhile at 537 C. a time of 72 seconds is necessary for 40% conversion at710 pounds per square inch pressure. The yield in this case is abouteight gallons of liquid product per 1000 cubic feet of stock charged.The product contains 90% gasoline which has an A. P. I. gravity of 64.0and a blending octane number (motor 4 method) of 93. The Englerdistillationfollosvs:

Percent loss z 2.0

It will be noticed that the yield of liquid in the first example is 10gallons per 1000 cubic feet of gas reacted while in the second case theyield is 8 gallons per 1000 cubic feet of gas reacted. In the firstexample the gas has an average molecular weight of 60 while in thesecond case the average molecular weight was 50. 'Ihus,-

the yield of liquid products is dependent on the molecular weight of thegas charged. For pure methane or pure ethane, the yield of liquid usingtheconditions described is zero. with pure propane (molecular weight 44)the yield is about two gallons per 1000 cubic feet of gas reacted. If onthe other hand the propane contains appreciable amounts of propylene(molecular weight 42), the liquid yield is higher. Thus, the yield ofliquid depends on the molecular weight of the gas charged and the amountof olefins present, since it is fairly easy to form liquids from theolefins already in the gas, while the formation of olefins from theparamns is accompanied by relatively large losses in the form ofnon-condensable" gases, particularly if the paramns have a. molecularweight of about 44.

.In each of the above examples each 1000 cubic feet of gas reacted.produced 1000-1300 cubic feet of non-condensable" gas as one of theproducts of reaction. This non-condensable" gas has a molecular weightof from 2540 and a heating value of 1500 B. t. u. per cubic foot.

The foregoing specification, as well as the examples of improved resultsobtainable by the use of the process, are given for illustrativepurposes only, and neither is to be construed as imposing limitationsupon the scope of theinvention.

What is claimed: a

1. A process for producing more valuable products from light hydrocarbonmaterial consisting essentially of hydrocarbons of 3 and 4 carbon atoms,which comprises subjecting said material, in admixture with recyclestock formed as hereinafter set forth, to pyrolytic conversion such asto convert a portion thereof into gasoline boiling hydrocarbons,controlling the reaction conditions of temperature, pressure and time inthe conversion step so that only from 20% to 50% by weight of saidmaterial undergoes alteration into hydrocarbons of less than 3 and morethan 4 carbon atoms, separating from the eiiluent of the conversion stepgaseous hydrocarbons of less than 3 ucts from light hydrocarbon materialconsisting essentially of hydrocarbons of 3 and 4carbon atoms, whichcomprises subjecting said material,

in admixture with recycle stock formed as hereinafter set forth, topyrolytic conversion at a temperature of from 450 C. to.575 C. andundera pressure of from 25 to 100 atmospheres for a time period suchthat onlyfrom 20% to 50% by weight of said material undergoes alteration intohydrocarbons of lessthan 3 and more than'4 carbon atoms, separating fromthe eilluent of the conversion step gaseous hydrocarbons of less than 3carbon atoms and isolating the same from the process, further separatingfrom said eilluent the 3 and 4 carbon atom hydrocarbons, supplying theseseparated 3 and 4 carbon atom hydrocarham to the conversion step as saidrecycle stock, and recovering the hydrocarbons of more than 4 carbonatoms from which the 3 and 4 carbon atom hydrocarbons have beenseparated.

3. A process for producing more valuable prod-.

ucts from ,the propane-butane fractions separated from hydrocarbon gasmixtures which comprises subjecting the propane-butane fraction, inadmixture with recycle stock formed as hereinafter set forth. topyrolytic conversion such as to produce gasoline boiling hydrocarbons,separating from the eiiluent of the conversion step an intermediatefraction consisting essentially of the 3 and 4 carbon atom hydrocarbonsof the eilluent, controlling the reaction conditions of temperature,pressure and time in the conversion step so that said intermediatefraction contains an amount of 3 and 4 carbon atom hydrocarbonscorresponding to from 50% to 80% by weight of said propane-butanefraction and so that said intermediate fraction contains not more than25% olefins, supplying said intermediate fraction to the conversion stepas said recycle stock, and isolating the remaining portion of saideilluent from the process.

4. A process which comprises subjecting a combined feed, formed ashereinafter set forth and consisting essentially of 3 and 4 carbon atomhydrocarbons, to pyrolytic conversion such as to convert a portionthereof into gasoline boiling hydrocarbons, separating from the eflluentof the conversion step an intermediate fraction consisting essentiallyof the 3 and 4 carbon atom hydrocarbons of the eiiluent, controlling thereaction conditions of temperature, pressure and time in the conversionstep so that said intermediate fraction contains not more than olefinichydrocarbons of 3 and4 carbon atoms, combining said intermediatefraction with the propane-butane fraction of a hydrocarbon gas mixtureand forming from these fractions a mixture containing less than olefinsand between and 80% by weight of the intermediate fraction, supplyingthe last-named mixture to the conversion step as said combined feed, andisolating'the remaining portion of saideflluent from the process.

5. A process for producing antiknock motor fuel from a normally gaseoushydrocarbon mixture having an average molecular weight between 50 and 80and comprised predominantly of paraffins of more than two and less thanfive carbon atoms per molecule, which comprises subjecting said mixtureto pyrolytic conversion such as to convert a portion thereof intogasoline boiling hydrocarbons, controlling the reaction conditions oftemperature, pressure and time in the conversion step so as to effectthe conversion of no more than 50% of the parafflns initially present insaid mixture, and separating from the eilluent of the conversion stepnormally liquid hydrocarbons in the gasoline boiling range.

ture having an average molecular weight between 50 and 60 and comprisedpredominantly of paraf fins of more than two and less than five carbonatoms per molecule which comprises subjecting said mixture to pyrolyticconversion at from 450 -to 575 C. and under pressure in excess of 500pounds per square inch for such a time as will eifect the conversion ofno more than 50% of the parafiins initially present in said mixture, andseparating from the efliuent of the conversion step normallyliquidhydrocarbons in 'the gasoline boiling range.

7. A process for producing antiknock motor fuel from a normally gaseoushydrocarbon mixture having an average molecular weight between 50 andz60and comprised predominantly of parafiins of more than two and less thanfive carbon atoms per molecule, which comprises sub- Jecting saidmixture to pyrolytic conversion at from 450 to 575 C. and under pressurein excess of 500 pounds per square inch for such a timeas will efi'ectthe conversion oi between20% and 50% of the paramns initially present insaid mixture, and separating from the efliuent oi, the conversion stepnormally liquid hydrocarbons in the gasoline boiling range.

8. A process for producing anti-knock motor fuel from a normally gaseoushydrocarbon material comprised predominantly of paramns of more than twoand less than five carbon atoms to the molecule, which process comprisesmixing said material with a recycle stock consisting of 3 and 4 carbonatom hydrocarbons, subjecting the mixture to pyrolytic conversion suchas to I convert a portion thereof into gasoline boiling hydrocarbons,controlling the reaction conditions of temperature, pressure and time inthe conversion step so that only from 20% to'50% by weight of saidmaterial undergoes alteration into hydrocarbons of less than 3 and morethan 4 carbon atoms, separating the eiiiuent oi the conversion step intoa fraction of normally liquid hydrocarbons, a fraction containing thehydrocarbons at less than 3 carbon atoms and an intermediate tractionconsisting of 3 and 4 carbon atom hydrocarbons, removing the first andsecond mentioned fractions from the process, and returning at least aportion of the intermediate fraction to the conversion step as saidrecycle stock. I

9. A process for producinganti-knock motor fuel from a normally gaseoushydrocarbon ma teriab comprised predominantly of parafiins'foi more thantwo and less than five carbon atoms to the molecule, which processcomprises mixing 7 said material with-a recycle stock consisting of 3and 4 carbon atom hydrocarbons, subjecting the mixture to pyrolyticconversion at a temperature of from-.460 C. to 575 C. and under apressure at from 35 tolooatmospheres for a time. period such that onlyfrom 20% to 50% by weight of said material undergoes alterationintohydrocarbonsoflessthan:iaiidmorethan4v carbon atoms, separating theeilluent of the conversion step into a fraction of normally liquidhydrocarbons, a fraction containing the hydrocarbonsorlessthan3carbonatom'sandanintermediate traction consisting oi 3 and '4 carbon atomhydrocarbons, removing the first and second mentioned fractions from theprocess, and returning at least a portion of the intermediate furthertreatment together with 'pyrolytic conversion such as to producegasoline boiling hydrocarbons, separating from the eilluent of theconversion step an intermediate fraction consisting essentially of the 3and 4 carbon atom hydrocarbons of theeiiiuent, controlling the reactionconditions of temperature, pressure and time in the conversion step sothat said intermediate fraction contains an amount of 3 and 4 carbonatom hydrocarbons corresponding to from 50% to 80% by weight of saidparafiinic fraction and so that said intermediate fraction contains notmore than 25% olefins, supplying said intermediate fraction to theconversion step as said recycle stock, and isolating the remainingportion of said efliuent from the process.

11. A process which comprises subjecting a combined feed, formed ashereinafter set forth and consistingessentially of 3 and 4 carbon atomhydrocarbons', to pyrolytic conversion such as to convert a portionthereof into gasoline boiling hydrocarbons, separating from the eilluentof the conversion step an intermediate fraction consisting essentiallyof the 3 and 4 carbon atom hydrocarbons of the eiiiuent, controlling thereaction conditions of temperature, pressure and time in theconversion'step so that said intermediate fraction contains not morethan 25% olefinichydrocarbons of 3 and 4 carbon atoms, combining saidintermediate fraction with a butane-containing, paraifin-predominatingfrac- .tion separated from a hydrocarbon gas mixture and consisting ofhydrocarbons of more than two and less than five carbon atoms to themolecule, said fractions being combined in such proportions as to form amixture containing less characterized in that there is additionallyseparated from said eilluent a fraction consisting of 3 and 4 carbonatom hydrocarbons which fraction is returned to the conversion step forbon mixture.

- 13. The process as defined in claim 6 further characterized in thatthere is additionally separated from said eiiiuent .a fractionconsisting of 3 and 4 carbon atom hydrocarbons which fraction isreturned to the conversion step. for

further treatment together with said hydrocarbon mixture.

said hydrocar- 14. The process as defined in claim '1 furthercharacterized in that there is additionally separated from said eiiiuenta' fraction consisting of3 and 4 carbon atom hydrocarbons which fractionis returned to the conversion step for further treatment together withsaid hydrocarbon mixture. c

I CARL W. von HILMOL'I',

Administrator de bo'nis mm with willannemed of Estate of Tropsch,

